DESCRIPTION OF THE RELATED ART
The present invention relates to a resonator arrangement for electron spin resonance spectroscopy having an annular resonance ring where the field lines of the resonance field emerge in the direction in the resonance ring axis and close in the outer space, and coupling means for coupling and decoupling microwave energy into and out of the resonance ring.
A resonator arrangement of the before-described type has been known before.
In electron spin resonance spectroscopy, an electromagnetic HF field is generated where the field lines of the magnetic field have a predetermined direction. One then introduces a sample into this area of the resonator. During this process, the resonator is placed in a constant magnetic field of high homogeneity and field strength with the field lines of this magnetic field standing perpendicularly on the field lines of the magnetic microwave field.
There have been known numerous resonator arrangements in this connection, i.e. cavity resonators, helix resonators, and strip line resonators of the most different shapes, and in some cases it is also possible to excite in such resonators oscillation modes of different orders.
One group of such resonators, which is used for electron spin resonance measurements, consists essentially of a dielectric resonance ring, i.e. a hollow-cylindrical structure consisting of a crystal, usually a sapphire, which is capable of oscillating freely in space. The field lines of the magnetic microwave field generated as a result of such oscillation pass through the axial bore of the dielectric resonance ring in axial direction and close in the outer space. It is, therefore, possible to introduce a sample into the central bore of the resonance ring, where the sample material is then passed by the--substantially axially directed--field lines of the magnetic microwave field.
There have further been known, in connection with resonator arrangements for electron spin resonance spectroscopy, numerous coupling arrangements by means of which a microwave signal can be coupled into the resonator arrangement, and the generated measuring signals can be coupled out. These coupling devices may be of an inductive or of a capacitive nature; there have been known numerous designs used for establishing the desired coupling. A very commonly used configuration of a coupling arrangement consists of a coupling loop, i.e. an antenna-like structure, by means of which the desired oscillation mode can be excited in the resonator arrangement from the outside.
In the case of the known resonator arrangements using a coupling loop the latter is arranged in that area of the resonator arrangement where the microwave field intended to influence the sample is directly excited. If, therefore, the known resonator arrangement comprises a cylindrical cavity in which a TE.sub.011 oscillation mode is excited, then the coupling loop may be located, for example, in a small end of the cylindrical hollow space in order to enclose in this area field lines which propagate at this point in radial direction.
Although such known resonator arrangements are well suited for many measuring applications, there also exist certain applications where resonator arrangements of this kind do not yield optimum results.
Pulsed electron spin resonance spectroscopy may be regarded as a typical example of such applications. In the case of this measuring technique, instead of feeding the microwave signal into the resonator in the form of a continuous-wave signal, the resonator arrangement is supplied with a pulsed microwave signal in order to examine specific dynamic processes in the sample.
It is a problem of this measuring technique that when a pulsed microwave signal is to be used, the resonator arrangement must have a large bandwidth. For, in the case of continuous-wave experiments the resonator Q may be, and should be, especially high in order to attain a good signal-to-noise ratio, whereas this is of course not the case with measurements using pulsed microwave signals that cover a broad frequency spectrum.